The image of George Jetson and family zipping about town is at once nostalgic and frustrating. Like George, most of us push buttons for a living. But so far, few of us commute in a flying car.

As with many of the technologies we "don't" have (where's my jetpack?), flying cars do exist. The roadable aircraft of today are basically small planes that can be driven legally down a road, usually because of a retractable-wing system.

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But, in a 2010 interview, physicist and science-fiction writer Gregory Benford summed up the problem with these designs: "It turns out that if you optimize the performance of a car and of an airplane, they are very far away in terms of mechanical features. So you can make a flying car. But they are not very good planes, and they are not very good cars."

Indeed, PM has rounded up the various contenders out there, many of which had creators who marketed them as the flying car we've all been waiting for. None, though, measures up to the vehicles of sci-fi: The Jetsons didn't lug a propeller around, which is how the Terrafugia Transition stays aloft. The famous Spinner in Blade Runner wasn't packing a jet turbine, which powers the current Moller Skycar.

When people ask for flying cars, they don't want planes that can drive on the ground. They really want cars that drive on the air, which would require some advanced manner of defying gravity. Perhaps magnetic levitation is the ticket; it uses the natural tendency of magnets with the same polarity to repel each other. Trains use this idea. Volkswagen's hyped concept hover car would use the same principle.

"One day, if we have room temperature superconductors, then our cars would float on a cushion of magnetism," theoretical physicist Michio Kaku said in an interview with PC Mag. "Our roads would be made of this superconductor; to get our cars going, all we have to do is blow on them, and they start to move. It would solve the energy crisis, since much of our oil goes into overcoming the friction of the road. "

But such vehicles would require an enormous infrastructure investment: a grid built over the roads to provide the magnetic force. Plus, what's the point? MagLev vehicles would stay just a few inches above the ground; they wouldn't zip around high in the sky like they do on Futurama. And they'd be tethered to the road network, which defeats the entire purpose of sci-fi-style flying cars.

To make vehicles like you see in cartoons, we'd essentially be building small planes that look like cars, which are expensive, awkward to fly, and create a host of new legal issues to deal with. (Do all drivers now need a pilot's license? And should drunk flying be a bigger crime than drunk driving?) Costs would be beyond astronomical, and, while they're not in the cold fusion realm of near-impossibility, high-temperature superconductors don't seem likely to emerge anytime soon. No one will blame you for keeping George Jetson's car on your wish list in the meantime.